Solid research shows that the smallest relevant biological unit of the microbiome is function, delivered by a network of intestinal bacteria. Bacteria need to interact in a functional network and achieve a balance so that the microbiome can work.
Characterization of the human genome and next generation sequencing of the intestine helped to uncover the important role of the gut bacteria in health and disease. The findings led to the realization that it may be possible to monitor, prevent or even cure human diseases through modulation of the microbiome.
A detrimental shift in intestinal microbiota composition (referred to as dysbiosis), mainly caused by external factors like antibiotics, diet or stress, but also genetic predisposition, can impair normal functioning of the gut and the connected organs. The major metabolic functions of the gut microbes include fermentation of non-digestible carbohydrates, synthesis of certain vitamins and synthesis of short-chain-fatty acids (SCFAs). Especially these SCFAs, mainly acetate, butyrate and propionate, are crucial for health, because they have both local and systemic anti-inflammatory effects and thus their loss mediates inflammatory responses. Interestingly, even though every individual has a unique bacterial fingerprint, the core functional groups and SCFA profiles are very conserved. During dysbiosis, dietary substrates are only partially degraded towards beneficial SCFAs, resulting in the accumulation of intermediate metabolites with detrimental effects.
This can lead to life-threatening infections or inflammatory diseases that can become chronic once the dysbiosis is established. Diseases with a clear link to the microbiome include local infections and inflammation but also systemic autoimmune, and inflammatory disorders (ulcerative colitis, carcinogenesis, obesity, rheumatoid arthritis, C. difficile infection or diabetes among others). Therefore, microbiome-related interventions have the therapeutic potential to sustainably re-establish a healthy state in the interaction of microbiome, the host’s gut epithelium and the immune-system and cure the multitude of diseases linked to dysbiosis.